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| Speed signalling v Route Signalling 01/12/2016 at 15:41 #89625 | |
KymriskaDraken
963 posts |
On the way home from work on the train last night something happened that made me thing about the pros and cons of speed signalling (as they have here in Sweden) compared with route signalling which is standard on the other side of the North Sea. The short version is that the train was wrong-routed at Stora Väsby by the Signalman (or ARS) in Stockholm. Instead of carrying on along the Up Slow (I don't know what the official name is, but it's heading North so it's Up - I know that much), past the junction for the airport, and on to Rosersberg, we turned left onto the airport line. Train comes to a stand, Driver gets out and walks to the other end (200m), drives back behind the junction signal, changes ends again, and off we go. Now, with route signalling the Driver would have got an advance indication that something wasn't right as he would have got an unusual aspect sequence leading up to the junction. For instance if he was routed onto the other line he probably would have got at least a yellow signal. COnversely if he was routed straight but wanted the junbction he would see clear signals where he wouldn't normally see them. In both cases he should be able to stop at the junction signal and query the route. Having said that there are, or at least were, junctions on the UK system where the signal sequence was identical for both directions - Bristol Parkway on the Down Badminton is one that caught me out as a Signalman several times. That particular signal's main routes (Down Filton or Down Tunnel) have the same speed and the signal doesn't have approach release for those routes. So, if you send one the wrong way the Driver doesn't know until he is almost on top of the signal as the old station footbridge was in the way. With speed signalling the Driver would ´possibly have been told to slow down for the junction instead of getting "fast" signals for the straight route, but I don't think the system can tell him why he needs to slow down, and that the aspect sequence for "slow down for the junction" is the same as "slow down as there is a red signal in front of you". Now, there are such refinements as ATC (with which Swedish railways are fitted) but even then I don't think that the Driver will know the reason why he is being told to slow down. So which system is best? Kev Log in to reply |
| Speed signalling v Route Signalling 01/12/2016 at 16:43 #89626 | |
clive
2789 posts |
KymriskaDraken in post 89625 said:Bristol Parkway on the Down Badminton is one that caught me out as a Signalman several times. That particular signal's main routes (Down Filton or Down Tunnel) have the same speed and the signal doesn't have approach release for those routes. So, if you send one the wrong way the Driver doesn't know until he is almost on top of the signal as the old station footbridge was in the way.Even worse was Colton Jn on the Up Fast. Again, both routes had the same speed and there is no approach release. So by the time the driver saw the lack of feather on the junction signal, it would be far too late to stop - he'd still be doing around 100 mph when the pantograph ran off the end of the wires. Log in to reply |
| Speed signalling v Route Signalling 01/12/2016 at 16:47 #89627 | |
Soton_Speed
285 posts 
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For the UK, I'm surprised that at the appropriate signals (i.e. not at the junction signal but where the equivalent of a flashing double yellow would be) a theatre route indicator is not fitted. I'm guessing that cost/benefit payoff of complication of the interlocking and the reduction in number of 'incidents' doesn't work out.
In Zone 6, no one can hear you scream... Log in to reply |
| Speed signalling v Route Signalling 01/12/2016 at 17:19 #89629 | |
Splodge
716 posts
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Preliminary Route Indicators are now appearing around the UK where there is otherwise no difference in indication for a specific route. http://www.railsigns.uk/sect6page5/sect6page5.html Locally they tend to only be going in where signalling systems are renewed, though most junctions I sign are indicated by flashing yellows for the appropriate route as the speed is lower on the diverging junction (Cheadle Hulme in the up direction - the Crewe route gets greens; the Stoke route gets flashing yellows on approach due to the low speed on the junction). There's the right way, the wrong way and the railway. Log in to reply |
| Speed signalling v Route Signalling 01/12/2016 at 18:36 #89631 | |
GeoffM
6376 posts
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KymriskaDraken in post 89625 said:With speed signalling the Driver would ´possibly have been told to slow down for the junction instead of getting "fast" signals for the straight route, but I don't think the system can tell him why he needs to slow down, and that the aspect sequence for "slow down for the junction" is the same as "slow down as there is a red signal in front of you".I'm trying to remember work I did on Norway which as similar signalling to Sweden, apart from a couple of aspects IIRC. If the two routes had different speeds then the junction signal would show red over green for the slower route and green over red for the faster route. The signal before that would have shown something restrictive that paired with the route at the junction signal but I cannot recall what that would have been. Let's say for the sake of example the first signal would have shown red over flashing yellow for the slower route and green over red for the faster route. So I would have *expected* the driver to have had advance warning but don't know the specifics at that location. However, it's not perfect as, for example, near here (in the US; speed signalling) all three diverging routes from a main line have exactly the same aspect, and only one leads to the passenger platform. Pros and cons to both speed and route really. SimSig Boss Log in to reply |
| Speed signalling v Route Signalling 01/12/2016 at 19:53 #89633 | |
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Forest Pines
525 posts |
KymriskaDraken in post 89625 said:The Deutsche Bundesbahn system still widely used in the former West Germany can because it was essentially a two-aspect system, with separate "stop signal" and "distant signal" heads. In the colour light version you often have both heads mounted on the same post; but the stop signal head will show "stop", "clear" or "slow" and the distant signal head below it will repeat the next stop signal (it gets more complicated if the next stop signal is less than a full braking distance away, but the idea is still the same). Therefore, the aspect sequence for "you are being routed onto a diverging track" is very different to "you are staying on this track but a signal ahead is at danger". Germany also uses indicators similar to British theatre indicators at key junctions to prevent significant wrong routing - they show a letter indicating which destination the train is being routed towards, rather than specifically which track it is being sent to. I don't know if they are fitted far enough in rear of junctions to allow trains to stop in time to prevent wrong-routing, though! Log in to reply |
| Speed signalling v Route Signalling 02/12/2016 at 09:48 #89647 | |
Bonan
55 posts |
I think that in this particular cause an observant driver with good route knowledge would have been able to stop in time. The Up Slow is 100mph and the points to cross over to the Up Fast (which becomes the airport line) are 80 mph, this would be shown both on the ATC system and in the signals, a flashing double green in the distant signal, "expect go 40" and a steady double green in the next main signal "go 40". 40 here being the speed in kmh allowed in case there is nothing else coming from the ATC, ATC would in this cause take authority over the signals by giving the driver 130 kmh in the display. Swedish driver and part-time signaller Last edited: 02/12/2016 at 09:51 by Bonan Reason: Typo Log in to reply |
| Speed signalling v Route Signalling 02/12/2016 at 20:23 #89659 | |
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KymriskaDraken
963 posts |
Bonan in post 89647 said:I think that in this particular cause an observant driver with good route knowledge would have been able to stop in time. The Up Slow is 100mph and the points to cross over to the Up Fast (which becomes the airport line) are 80 mph, this would be shown both on the ATC system and in the signals, a flashing double green in the distant signal, "expect go 40" and a steady double green in the next main signal "go 40".I don't know how the Swedish ATC system works, but I would expect it to say that the Driver needed to slow to 80 for the points, and then (assuming the line ahead to be clear) step up to the line speed for the airport line. I can't quite see how the Driver can tell the difference between being told to slow for a junction, or slow because a signal is at Danger. I suppose it really all depends on how far ahead the ATC equipment can "see", and how often the information gets updated. Kev Log in to reply |
| Speed signalling v Route Signalling 02/12/2016 at 21:01 #89661 | |
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Bonan
55 posts |
The Swedish ATC system has two 3-digit screens, one showing the current maximum speed and the other one upcoming lower speed restrictions. An upcoming signal at danger would simply be shown as "0", and the proceeding distant signal would show "expect stop", a single flashing green. The driver should be able to tell that something is amiss when he gets the upcoming 80 mph restriction in the ATC system and sees the double green flashing distant signal, as there isn't any such restriction on the Up Slow. However, he could also been routed onto the Down Slow for whatever reason and as that would look the same to the driver I understnad how he could have missed it. I was once routed onto the line towards Västerås instead of the main line towards Uppsala, and in that case with a loco-hauled train. I don't remember exactly, but the delay got well above one hour in the end, as the loco had to run around the train twice. I know that a direction signal has been installed in either end of the new City Tunnel, as only a few train classes are allowed to access it. Swedish driver and part-time signaller Last edited: 02/12/2016 at 21:02 by Bonan Reason: Typo Log in to reply The following user said thank you: KymriskaDraken |